You are probably familiar with news reports of a jackknifed semi. Often when this happens, it closes a roadway and causes traffic disturbances. Sometimes, it is a limited situation with no injuries or damage to other vehicles, but on occasion, it can be a serious situation involving pile ups and loss of life. In any case, a jackknifed semi is a huge issue that is usually preventable.
HowStuffWorks explains that jackknifing occurs when the cab of the semi folds against the trailer. It forms a “V” shape, which looks much like a jackknife and gives the situation its name. The truck ends up in this situation when the trailer and the cab get out of sync somehow. In most situations, this happens due to a loss of traction.
Jackknifing is more common on slick roadways because traction is not as good when the roadway is wet as when it is dry and tires cannot grip as well. If the semi’s tires begin to slide on the road, it is easy for the cab to slow and the trailer to keep moving at the prior speed or for the trailer to speed up while the cab remains at the prior speed. This takes both parts of the semi out of sync and leads to the trailer going ahead of the cab, which then turns around due to the force of the trailer moving past it.
This can also happen if a driver practices bad breaking habits. Slowing the cab too quickly with hard breaking will lead to the trailer not having enough time to slow down. Thus, it continues past the cab, causing the jackknifing.